1. Field of the Invention
The present general inventive concept relates to a paper feeding cassette of an image forming apparatus which stacks sheets of paper and can be attached or detached to or from a main body.
2. Description of the Related Art
In general, an image forming apparatus, such as a printer, a copier, or a multifunctional device, includes a paper feeding cassette which stacks a sheet of paper inside of the paper feeding cassette and is attached or detached to or from a main body. A paper stacking plate is installed inside the paper feeding cassette to lift the sheet of paper that is stacked on the paper stacking plate. Thus, the paper stacking plate allows the sheet of paper to contact a pickup roller installed in the main body, and the sheet of paper is picked up and transferred to an inside of the main body when the pickup roller is rotated.
A method of lifting the paper stacking plate in the paper feeding cassette is performed in two ways. First, the paper stacking plate is elastically biased in an upward direction by an elastic force of an elastic unit, such as a spring installed under the paper stacking plate. When a plurality of sheets of paper is stacked on the paper stacking plate, the paper stacking plate is lifted by the weight of the paper. This method is generally used in a case where an amount of the paper stacked on the paper feeding cassette is small. Second, when the amount of the paper stacked on the paper feeding cassette is large, like in a large copier, the weight of the paper cannot be supported using the elastic force of the elastic unit such as the spring. Thus, an additional device to lift the paper stacking plate is needed. In this method, an additional lift plate connected to a driving motor is used so that the lift plate is ascended and descended under the paper stacking plate.
U.S. Pat. No. 5,100,122 discloses an invention having the above structure. That is, a knock-up plate to stack paper in a feed cassette is installed, and a lift plate is installed under the knock-up plate while being fixed in a rotating pivot. A gear is installed at one side of the rotating pivot and is engaged with a gear installed in a lift plate driving motor.
The rotating pivot is rotated by a rotating force of the lift plate driving motor. The knock-up plate is lifted when the rotating pivot is rotated together with the lift plate. Then, the paper contacts a pickup roller installed above the paper feeding cassette. In this case, a sensor senses whether the paper is in contact with the pickup roller and allows the operation of the lift plate driving motor to stop when the paper contacts the pickup roller.
A frictional force by which the paper is picked up using the pickup roller is generated by a force by which the lift plate, based on the rotation of the lift plate driving motor, lifts the paper stacking plate.
However, when a controller does not control the lift plate driving motor, and the lift plate driving motor operates continuously although the sensor senses that the paper has contacted the pickup roller, the knock-up plate lifts continuously, and the paper is excessively pressed against the pickup roller. Furthermore, an operation of detaching the paper feeding cassette from the main body may not be performed smoothly.